PROJECT SUMMARY/ABSTRACT Despite being a leading cause of death and morbidity in the U.S., ischemic stroke still has limited therapeutic options. In recent years, the protective potential of pre-conditioning has attracted much attention, though given the difficulty in predicting when stroke will occur, its application to preventing stroke in the general population is somewhat limited. However, there are several clinical scenarios where for a period of time, the risk of stroke is dramatically increased, including cardiac/vascular surgery, and recent history of stroke or transient ischemic attack. In these common scenarios, short-term protection conferred by pre-conditioning may offer considerable clinical potential. While the benefit of hypoxic pre-conditioning against stroke has been known for many years, only recently has the neuroprotective effect of a ketogenic diet been demonstrated. While this neuroprotection has largely been attributed to improving metabolic efficiency, thus far, no-one has examined the vascular contribution to this protection. In this R21 application, we hypothesize that a ketogenic diet protects against ischemic stroke by promoting blood-brain barrier (BBB) integrity via increased expression of endothelial tight junction proteins and the vasculo-protective integrin ?6?4. This hypothesis is supported by several observations. First, like mild hypoxia, a ketogenic diet promotes profound angiogenic remodeling in the brain, along with increased expression of key BBB transporter molecules. Second, also like mild hypoxia, a ketogenic diet activates hypoxia-inducible factor (HIF)-1? signaling, suggesting that these two stimuli may achieve neuroprotection via common downstream mechanisms. Third, mild hypoxia upregulates endothelial expression of tight junction proteins, implying that one mode of action of these pre-conditioning stimuli is to promote BBB integrity. Last, we have shown that the endothelial extracellular matrix integrin receptor ?6?4 is upregulated during hypoxic conditioning, and appears to enhance BBB integrity. To test our hypothesis, we propose three specific aims: (1) demonstrate that a ketogenic diet promotes cerebral angiogenesis and increased endothelial expression of vascular remodeling integrins and tight junction proteins, (2) demonstrate that ketogenic-conditioned mice are resistant to ischemic stroke due to enhanced BBB integrity through upregulation of endothelial tight junction proteins and ?6?4 integrin, and (3) define the roles of the angiogenic (?5?1) and stabilizing (?6?4) integrins in mediating vascular remodeling in response to a ketogenic diet. These studies will characterize for the first time, the cerebrovascular remodeling events induced by a ketogenic diet and define the contribution of this remodeling to protection from ischemic stroke. We expect to demonstrate that a ketogenic diet promotes robust cerebrovascular remodeling and that ketogenic-conditioned mice will be resistant to ischemic stroke, in part due to enhanced BBB integrity via increased endothelial expression of the vasculo-protective integrin ?6?4 and tight junction proteins. Successful completion of these studies could lead to the development of a novel approach for preventing ischemic stroke in high-risk patients.